Pro-Grid vertical grid D.E. filters provide superior water clarity, efficient flow and large cleaning capacity for pools and spas of all types and sizes. Constructed with high-strength reinforced thermoplastic, Pro-Grid combines high-technology features and "service-ease" design for an unparalleled filtration value for both new pool and aftermarket installations.How A Vertical Grid D.E. Filter WorksUniform Low Profile Tank Base make removal of grid nest fast and simple. High-Strength Filter Tank molded of reinforced thermoplastic provides extra durability for dependable, corrosion-free performance. Glass-filled polymer Bulkhead Fittings for extra strength and heat resistance. High Impact Grid Elements designed for up-flow filtration and top-down backwashing for maximum efficiency. Heavy-Duty Tamper-Proof Bolted Center Flange Clamp securely fastens tank top and bottom together. Allows quick access to all internal components without disturbing piping or connections. Union Locknuts make disassemble and reassemble of filter from piping fast and easy. Inlet Diffuser Elbow distributes flow of incoming unfiltered water upward and evenly to all filter elements. Parabolic tank design provides for even distribution of D.E. to grids. Full-Size 1.5" Integral Drain provides fast, 100% clean out and easier flushing of tank. Convenient Valve and Plumbing Options allow for customized control. 2" internal piping and plumbing for maximum flow performance.See below to read the differences between D.E. and Cartridge filters.D.E. vs Cartridge FiltersDE is always a much better filter; it will filter about 10 times finer particles than cartridge will. Cartridge filters need to be cleaned every few months, whereas DE filters can usually go month or two longer for similar sized filters. Backwashing is not recommended, but you want to you can. If a DE filter is properly sized (48 or 60 sq ft for most residential pools) they will usually only need to be cleaned 2 times a year. Without the help of cellulose, a cartridge filter will have a very difficult time filtering out algae (should the pool get it which all pools do),when you add one of these products it's basically like putting DE in a cartridge filter. Your other option is to add a flocculent, which will clump the particles so they are bigger and the cartridge will filter them out, with a flocculent you are making the particle bigger and with cellulose you are adding an additive to allow the filter to filter out finer particles. The only advantages to cartridge are that they are slightly more customer friendly and slightly easier to clean, mostly because you don't have to add DE when you are done cleaning it. The assembly (putting the filter back together) is also a little bit easier. This should not influence anyone's decision as to which one is better, and should be purchased. A lot of builders use cartridge filters because many cities require them, or they don't allow DE on new construction. The reason for that is that DE is not good for the environment. Almost 100% of the filters purchased by the service trade are DE, because they work MUCH better. Also, the life expectancy of a grid (DE) is about 10 years if they are taken care of (backwashing will decrease the life expectancy because it stretches the cloth on the grid), a cartridge is only expected to last 3-5 years. Replacement cartridges also cost about double what a new set of grids would.Basic Pool & Spa Combination Plumbing Diagram